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Temperature gauge is pegged while cold

Hi,
I just replaced my radiator on my 2000 540i, when I started the engine, the temperature gauge immediately was pegged full scale. It worked fine until I changed the radiator. Does anyone have any idea what could cause this? I don;t have a wiring diagram available, is this the fault mode for open wiring or a short? Thanks.

Re: Look at the temp sensor on top of the T-Stat (m)

When I first started the car, I forgot to plug it in. I plugged it in, and it was pegged full scale. I thought perhaps I got something in the sensor socket so I cleaned it out with electrical part cleaner, but it didn't make any difference. Is it easy to damage this sensor? Is there any way I can test the plug to make sure I didn't open the wiring when I pulled it off? Thanks.

If you have an ohm meter you can check the sensor(

There are 4 pins in the coolant temp sensor.
One sensor for the DME, pins 3 & 4 read 2.5K ohms at 20°C.
The other sensor is for the temp gauge in the cluster, pins 1 & 2 read 6.3K ohms at 20°C.
As mlane said the resistance goes down as the sensor heats up which makes the gauge read hotter. You could have a short somewhere.

Re: If you have an ohm meter you can check the sensor(

Whether the sensor is plugged in or not, the gauge still goes to full scale. I measured the resistance at about 0 C, the reading between pins were about 6.5k and 16.5k, so I have to assume the sensor is good. With the ignition off, I measured the resistance across the pins of the connector, I didn't see any dead shorts. All I did was unplug the sensor to remove the intake duct, then when I started the car initially, I forgot to plug the sensor back in. How is it possible to cause a short or damage an input? I guess it's possible I might have tugged on the cable and could have caused an open but from what everyone says, that would result in the temperature indicator never going up. Anyone have any other ideas? Thanks.

Disconnect both battery cables and connect (m)

the cables together. Then turn the key to the run position for 10 minutes. Maybe you scrambled the memory in the cluster by not connecting the sensor. This should drain any incorrect data.
Let us know how you make out.